This invention relates to doors which seat into door frames, and in particular to guides which facilitate closure and centering of a door within the door frame of a semiconductor wafer transport module.
Semiconductor wafers are subjected to numerous steps during processing. This usually entails transporting a plurality of wafers from one workstation to another for processing by specialized equipment. As part of the processing procedure, wafers may be temporarily stored or shipped in containers to other plants or to end users. Such intra and extra movements may generate or expose the wafers to potential wafer ruining contaminants. In order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. A principal feature common to these devices is that they are provided with removable doors or closures.
There are several problems associated with the above-mentioned wafer handling devices or containers. During the working life of a container, the closure or door is attached and removed many times by both robotic and manual means. With each attachment and removal, a portion of the door edge may scrape against the door frame of the container. This can result in the generation of loose particles which may become airborne to lodge on the wafers being contained.
Equally important, doors of wafer handling devices or containers typically include cushions or channels which contact and support wafer edges. Optimally, such cushions or channels are designed to operate in concert with wafer receiving channels in the containers to securely retain a plurality of wafers. If a door is not, and cannot be accurately and repeatedly centered within a door frame, excessive contact and subsequent particle generation between the door cushions or channels and wafers may occur.
The problem of particle generation may also be attributed to the process by which doors and containers are manufactured. Containers and doors are usually formed by injection molding with plastic such as polycarbonate. Inherent in such molding is shrinkage and warpage of the molded parts. Although plastic injection molding techniques are highly advanced, there still may be individual deviations between different components form the same mold. While slight deviations do not generally compromise the function of a door in closing an container, they can change the working dimensions to the extent that contact (and the resultant particle generation) between a door and a door frame is increased. Dimensional changes can also be generated by the dies themselves, as a result of normal wear and tear. This problem is accentuated when the tolerances of the components of doors and containers are stacked or added.
As the semiconductor industry has evolved, wafers, and thus wafer carriers have increased significantly in size. Semiconductor fabrication facilities are now processing 300 mm wafers. With the larger carriers for 300 mm wafers, the warpage, shrinkage, and tolerance issues in molded carriers are amplified.
Yet another problem occurs because these wafer carriers are robotically opened and closed. The carriers will be opened by multiple pieces of equipment which may each be set up slightly different. Also such equipment may go out of adjustment and is subject to wear and tear. Such equipment may not then be perfectly aligned resulting in undesirable and/or excessive door-frame contact and a situation of excessive abrasion and/or particle generation.
The present invention ameliorates the problems inherent to the above-mentioned wafer containers by providing low particle generating guides which may be attached to the edge of a container door.
A semiconductor wafer carrier has an enclosure with a door frame defining an opening for insertion and removal of wafers, a door for closing and sealing said opening, and separately formed door guides for controlling the interface between said door and the enclosure. In a preferred embodiment, the door guides each comprise a first body and a second body connected to each other by a web. Each body includes a door contacting portion and a door frame contacting portion. The door frame contacting portion has a sloped segment configured to slidingly, progressively, and cooperatively engage the door frame to properly position the door within the door frame during closure with minimal particle generation by such contact. In this preferred embodiment, the guide is configured to be attached onto a corner edge of a door. In this arrangement, as the door is inserted into the door frame in the z-direction, the first and second bodies exert centering forces as needed in the x and y directions on corner portions of the door. Such centering forces are provided with minimal particle generation due to low particle generating characteristics of the guides.
In a preferred embodiment, the sloped segment of a body is designed to progressively engage or urge a door away from a door frame as the door is centered and/or seated in the door frame. The preferred sloped segment has two surface portions with different camming efficiencies, or slopes, with a first surface portion having a relatively larger slope when compared to the second surface portion. Although the preferred sloped segment is depicted as having two generally linear surfaces, it is understood that other surface profiles may be used. For example, the sloped segment could be a single linear camming surface or a nonlinear camming surface in the form of an arc or involute.
When a plurality of bodies have been positioned at appropriate locations around the perimeter of a door, they work in concert with each other to effectively, accurately and quickly center and/or seat a door within a frame. That is, when guides having first and second bodies are attached at each corner of a door, the ends of each facet or side of the door are effectively urged away from a corresponding door frame facet or side by a similar distance, thus entering the door within a door frame.
In a preferred embodiment, the web, which connects the first and second bodies to each other, may perform several functions. One function is to position the first and second bodies for optimum effectiveness. That is, positioning the door contacting surfaces of the first and second bodies against the door, and positioning the door frame contacting surfaces of the first and second bodies so that they project toward the door frame edge. Another function of the web is to attach and retain the guide on the edge of a door. Attachment of a guide onto a door edge is achieved through interaction of the first and second bodies as they are biased against notches in the door edge. Specifically, the door contacting portions of the first and second bodies each include an engagement portion which extends along the inwardly facing length of each body. These engagement portions are configured to be received in collateral notches formed in the sides or facets of the door and retained in their respective notches by the biasing force exerted by the resilient web. A guide may be attached onto a corner of a door by flexing the web and snapping the engagement portions into their respective notches, in the manner of a spring clip. Thus no external fasteners are required for the attachment.
In preferred embodiments, the guides are preferably composed from a mixture of polyetheretherketone (PEEK) and polytetrafluorethylene (PTFE) in ratios of around 80% and 20%, respectfully. This material is relatively harder than the typical door and/or container material such as polycarbonate. Moreover, it has very favorable particle generating characteristics minimizing particle generation during door-edge to door-frame engagement. It also, by virtue of its relatively low level of frictional resistance, reduces the level of force needed to insert and remove a door from a container.
While the guide of a preferred embodiment of the invention comprises a first body and a second body connected to each other by a web, alternative embodiments are within the scope of the invention. For example, the guide may comprise a singular body or a train of bodies which are attachable onto the door at various locations such as the sides, corners or a combination of sides and corners. Moreover, attachment of the guide or guides need not be restricted to the biasing action of an arcuate web which causes portions of the first and second bodies to be retained on the door. Other embodiments could utilize, for example, complementary fasteners, adhesives, weldments, and threaded fasteners.
There may be instances where the fit between a door and a door frame is less than ideal, and the seam or space between a door and door frame varies slightly. For example, a door and/or door frame may be warped or skewed with respect to each other. Such an irregular seam or fit may prevent optimal centering of the door within a frame using a set of similarly sized guides. In such instances, the guides may be available in an array of varying sizes to permit optimal positioning of a particular door within a particular door frame.
In alternative embodiments, the guides may be attached to the door frames in addition to or rather than the doors. Where the guides are attached to both the door and door frame, the guides may be attached in an offset or face to face cooperating relation.
It is a object of particular embodiments of the present invention to provide the door of a wafer container with removable door guides.
Another object of particular embodiments of the present invention is to reduce the amount of particulates generated by frictional contact between a door and a door frame.
Another object of particular embodiments of the present invention is to facilitate centering of a door within a door frame.
Yet another object of particular embodiments of the present invention is to reduce the amount of particulates generated by frictional contact between door mounted cushions and semi-conductor wafer edges.
Still another object of particular embodiments of the present invention is to increase permissible tolerances between a door and a door frame.
An advantage of particular embodiments of the present invention is that guides may be removably attached at various locations on a door.
A feature of the particular embodiments of the invention is that the guides are fabricated out of a relatively hard and low friction material which resists wear.
Additional objects, advantages, and features of various embodiments of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of various embodiments of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.